Displays are used in televisions and computers. Projectors are most commonly used in televisions. Display types include cathode ray tubes (CRTs) and liquid crystal displays (LCDs). CRTs use electron beam technology that has been present for many years in consumer products such as television (TV) tubes and computer monitors. CRTs use hot cathode electrodes to create a source of electrons that are directed to and focused on the viewing screen. The viewing screen generally includes glass. Directing the electrons to the viewing screen requires some distance. In addition, the viewing screen is generally made of glass, so CRTs are heavy, especially in larger displays or monitors. Consequently, CRTs are heavy and use a relatively large space when compared to LCD monitors.
LCD monitors are lightweight and thin in comparison to CRTs. An LCD may use two pieces of polarized glass. A special polymer is dispensed on a side of the glass that does not have a polarizing film on it. A special polymer creates microscopic grooves in the glass surface to form a first light filter. The grooves are in the same direction as the polarizing film. The grooves are coated with pneumatic liquid crystals to finish a light filter. The grooves cause the first layer of molecules to align with the filter's orientation. The second piece of polarized glass is supported by the first piece of polarized glass at a right angle. Each successive layer of molecules gradually twists until the uppermost layer or portion of the molecule is at a 90-degree angle to the bottom layer or portion. The twisted molecules, therefore, act as light guides that twist to match the polarized glass filters.
As light strikes the first filter, it is polarized. The molecules in each layer then guide the light they receive to the next layer. As the light passes through the liquid crystal layers, the molecules also change the light's plane of vibration to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. If the final layer is matched up with the second polarized glass filter, then the light may pass through.
Applying an electric charge to the liquid crystal molecules causes the molecules to straighten out or untwist. When they straighten out, they change the angle of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no light can pass through that “charged” area of the LCD, which makes that area darker than the surrounding areas. LCDs switch pixels through polarization.